dm mpath: free path selector on invalid args

Free path selector if the arguments are invalid.

This command (note that it is invalid) causes reference leak on module
"dm_round_robin" and prevents the module from being removed.

dmsetup create --table '0 2 multipath 0 0 1 1 round-robin /dev/sdh' mpath0

Signed-off-by: Mikulas Patocka <[e-mail]>
Signed-off-by: Alasdair G Kergon <[e-mail]>

drivers/md/dm-mpath.c

···
 	}
 
 	r = read_param(_params, shift(as), &ps_argc, &ti->error);
-	if (r)
+	if (r) {
+		dm_put_path_selector(pst);
 		return -EINVAL;
+	}
 
 	r = pst->create(&pg->ps, ps_argc, as->argv);
 	if (r) {